1. Field of the Invention
The present invention relates to a method and a device for operating an internal combustion engine, in which a setpoint fuel-injection quantity is subdivided.
2. Description of Related Art
Already known in the art are methods and devices for operating an internal combustion engine, in which a setpoint fuel quantity to be injected is subdivided into a first fuel quantity to be injected into an intake manifold, and into a second fuel quantity to be injected directly into a combustion chamber of the internal combustion engine, as a function of a temperature that is characteristic for the operation of the internal combustion engine in a start of the internal combustion engine. Depending on the engine temperature characteristic for the operation of the internal combustion engine, for example, a distinction is made between a cold start and a warm start of the internal combustion engine. In the cold start, it is known from the market to inject the setpoint fuel quantity to be injected solely via the first fuel quantity to be injected, into the intake manifold of the internal combustion engine. For the warm start, on the other hand, it is known to inject the setpoint fuel quantity to be injected solely via the second fuel quantity to be injected, directly into the combustion chamber of the internal combustion engine. The reason for this is a better mixture carburetion with the aid of the intake manifold injection in the cold start and reduced self-ignition and knocking tendencies in case of a direct injection into the combustion chamber in the warm start.
Fuel that is introduced into the intake manifold during the start of the internal combustion engine with a cold engine deposits on the walls of the intake manifold, does not fully evaporate, and therefore does not take part in the starting combustions. In order to ensure a stable engine run-up, an increased fuel mass is therefore required in the start phase.
At cold start temperatures of approximately 20° C., the proper homogenization of the air/fuel mixture of an intake manifold injection manifold injection already in front of the combustion chamber of the internal combustion engine results in low emissions, in particular of hydrocarbons, in comparison with a direct injection during the intake stroke of the internal combustion engine. An intake manifold injection is therefore advantageous in a cold start. At higher temperatures, a direct injection during the intake stroke of the internal combustion engine leads to reduced temperatures in the cylinder due to the evaporation of the fuel in the combustion chamber, and thus to lower knocking and self-ignition tendencies.
A dropping engine temperature or ambient temperature in a cold start of the internal combustion engine increases the wall film formation in the injection in the intake manifold, so that the fuel supply must be increased further. As a consequence, the undesired emissions of hydrocarbons, for example, rise during the start of the internal combustion engine.